The purpose of this project is to investigate the genetic regulation of the galactose catabolic enzymes, galactokinase, galactose-1-phosphate uridyltransferase and UDP-galactose-4-epimerase in a mammalian cell culture system. The levels of these three enzymes will be determined in cells growing in glucose and compared to the activities in galactose grown cells. This will be done both in normal human diploid fibroblast and SV-40 transformed fibroblast cultures. The enzyme levels in rat liver cells will also be investigated. Differences in enzyme activities will be determined in both log phase and stationary phase cell growing in glucose or galactose. This biochemical pathway is of special clinical importance because of the genetic disease associated with deficiencies in either the kinase or transferase enzyme. The effects of these enzyme deficiencies on other enzymes in the pathway will also be investigated in cells deficient in only one enzyme and in hybrids formed between kinase and transferase deficient cells. Elucidation of the mechanisms responsible for the genetic regulation of the galactose catabolic enzymes will be important in increasing our general understanding of how enzyme amounts are controlled and will provide basic information important to the study of galactosemia.